U.S. patent application number 17/445785 was filed with the patent office on 2021-12-16 for parametric light generation method and its application.
The applicant listed for this patent is SHAN DONG UNIVERSITY. Invention is credited to Xun SUN, Zhengping WANG, Xinguang XU, Fapeng YU, Xuezhi ZHAO.
Application Number | 20210389644 17/445785 |
Document ID | / |
Family ID | 1000005851892 |
Filed Date | 2021-12-16 |
United States Patent
Application |
20210389644 |
Kind Code |
A1 |
WANG; Zhengping ; et
al. |
December 16, 2021 |
Parametric Light Generation Method and Its Application
Abstract
The invention is related to a parametric light generation method
and its application and belongs to the technical field of laser and
nonlinear optics. The generation method comprises steps as follows:
a nonlinear optical material that meets the sum-frequency
phase-matched conditions, namely it shall satisfy the energy
conservation condition .omega..sub.p+.omega..sub.i=.omega..sub.s
and the momentum conservation condition
n.sub.p.omega..sub.p+n.sub.i.omega..sub.i=n.sub.s.omega..sub.s
simultaneously, is provided; laser light with a wavelength of
.lamda..sub.p is injected into the said nonlinear optical material
as pump light; then, the material will output signal light with a
wavelength of .lamda..sub.s, namely the tunable sum-frequency
parametric light. With sum-frequency as the basic principle, the
invention can realize frequency up-conversion and obtain visible
and UV light sources through simple infrared light sources
easily.
Inventors: |
WANG; Zhengping; (Jinan,
CN) ; ZHAO; Xuezhi; (Jinan, CN) ; YU;
Fapeng; (Jinan, CN) ; SUN; Xun; (Jinan,
CN) ; XU; Xinguang; (Jinan, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHAN DONG UNIVERSITY |
Jinan |
|
CN |
|
|
Family ID: |
1000005851892 |
Appl. No.: |
17/445785 |
Filed: |
August 24, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 3/0092 20130101;
G02F 1/392 20210101 |
International
Class: |
G02F 1/39 20060101
G02F001/39; H01S 3/00 20060101 H01S003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2020 |
CN |
202010964346.9 |
Claims
1. A parametric light generation method, which comprises steps as
follows: a nonlinear optical material that meets the sum-frequency
phase-matched conditions is provided, that is, it shall satisfy the
energy conservation condition
.omega..sub.p+.omega..sub.i=.omega..sub.s and the momentum
conservation condition
n.sub.p.omega..sub.p=n.sub.i.omega..sub.i+n.sub.s.omega..sub.s
simultaneously, where s denotes signal light, p denotes pump light,
and i denotes idle frequency light; laser light with a wavelength
of .lamda..sub.p is injected into the said nonlinear optical
material as pump light. Then, the material will output signal light
with a wavelength of .lamda..sub.s, namely the tunable
sum-frequency parametric light.
2. The said parametric light generation method according to claim
1, characterized in that the sum-frequency phase-matching
conditions can be changed continuously by adjusting the space
direction, temperature, voltage, or microstructure parameters of
the nonlinear optical material to realize the continuous change of
.lamda..sub.s and the output of the tunable sum-frequency
parametric light.
3. The said parametric light generation method according to claim
1, characterized in that light waves with wavelengths of
.lamda..sub.i and .lamda..sub.s are generated and amplified
spontaneously by the nonlinear optical material through parametric
scattering or parametric fluorescence; or, light waves with
wavelengths of .lamda..sub.i and .lamda..sub.s are generated and
amplified spontaneously by the nonlinear optical material through
parametric scattering or parametric fluorescence, and, in the
resonant cavity formed by adding cavity mirrors at both ends of the
nonlinear optical material, the signal light will make multiple
round trips to gain significantly enhanced output; or, signal light
.lamda..sub.s, .lamda..sub.p, and .lamda..sub.s with lower energy
are provided at the input end, and they will interact with each
other on the premises of satisfying the sum-frequency
phase-matching conditions to amplify the signal light significantly
at the output end at the cost of consuming the pump light.
4. The said parametric light generation method according to claim
1, characterized in that the said nonlinear optical material is a
bulk crystal with a single structure, a crystal with a periodic
structure that can realize quasi-phase matching, an ordinary
optical fiber, or a photonic crystal fiber.
5. The said parametric light generation method according to claim
4, characterized in that the said bulk crystal is GdCOB, YCOB, KDP,
or BBO.
6. The said parametric light generation method according to claim
1, characterized in that the pulse laser is to be used as the pump
light.
7. The said parametric light generation method according to claim
1, characterized in that the pump light is to be focalized or
reduced in beams for space shaping to boost its power density and
improve the output energy and conversion efficiency of the signal
light.
8. The said parametric light generation method according to claim
1, characterized in that the 1540 nm femtosecond laser is to be
used as the pump light: when the nonlinear optical material is a
GdCOB crystal processed along (.theta.=146.degree.,
.PHI.=0.degree.), the tunable laser output at the visible waveband
of 485-770 nm can be obtained by rotating the crystal to adjust the
sum-frequency phase-matching conditions; when the nonlinear optical
material is a YCOB crystal processed along (.theta.=140.degree.,
.PHI.=0.degree.), the tunable laser output at the visible waveband
of 450-770 nm can be obtained by rotating the crystal to adjust the
sum-frequency phase-matching conditions.
9. The said parametric light generation method according to claim
1, characterized in that the 1056 nm femtosecond laser is used as
the pump light, and when the nonlinear optical material is a YCOB
crystal processed along (.theta.=149.degree., .PHI.=0.degree.), the
tunable laser output at the visible waveband of 425-528 nm can be
obtained by rotating the crystal to adjust the sum-frequency
phase-matching conditions; or, the 1056 nm femtosecond laser is
used as the pump light, and when the nonlinear optical material is
a KDP crystal processed along (.theta.=41.degree.,
.PHI.=45.degree.), the tunable laser output at the visible waveband
of 390-670 nm can be obtained by rotating the crystal to adjust the
sum-frequency phase-matching conditions; or, the 1053 nm
femtosecond laser is used as the pump light, and when the nonlinear
optical material is a .beta.-BBO crystal processed along
(.theta.=23.degree., .PHI.=30.degree.), the tunable laser output at
the visible waveband of 185-526.5 nm can be obtained by rotating
the crystal to adjust the sum-frequency phase-matching
conditions.
10. Any of the following applications of the said parametric light
generation method according to claim 1: the sum-frequency
parametric light generation of the lithography machine (193 nm) and
the medical diagnosis and radiation treatment (325 nm); the
dual-wavelength sum-frequency parametric light generation of the
ultraviolet differential absorption laser radar; the
dual-wavelength sum-frequency parametric light generation of the
hemoglobin detection in carbon monoxide poisoning; the
dual-wavelength sum-frequency parametric light generation for the
treatment of intractable port-wine stains; the sum-frequency
parametric light generation of the white light laser.
11. A parametric light generator which comprises a pump light
source and a nonlinear optical medium sequentially arranged along
the optical path; the nonlinear optical medium satisfies the energy
conservation condition .omega..sub.p+.omega..sub.i=.omega..sub.s
and the momentum conservation condition
n.sub.p.omega..sub.p+n.sub.i.omega..sub.i=n.sub.s.omega..sub.s
simultaneously, where s denotes signal light, p denotes pump light,
and i denotes idle frequency light.
12. The said parametric light generating device according to claim
11, characterized in that a focusing lens is also provided between
the pump light source and the nonlinear optical medium.
13. The said parametric light generating device according to claim
12, characterized in that a color filter is also arranged behind
the nonlinear optical medium along the light path; preferably, an
input mirror of optical parametric oscillation is provided between
the focusing lens and the nonlinear optical medium along the light
path, and an output mirror of optical parametric oscillation is
provided behind the nonlinear optical medium.
14. The said parametric light generating device according to claim
12, characterized in that a signal light source, a signal light
reflecting mirror, and a beam combiner for the pump light and the
signal light are also provided to enable the signal light generated
by the signal light source to enter the focusing lens together with
the pump light generated by the pump light source upon the
reflecting of the signal light reflecting mirror and the combining
of the beam combiner for the pump light and the signal light.
15. The said parametric light generating device according to claim
12, characterized in that behind the nonlinear optical medium is
provided the second nonlinear optical medium along the optical
path, between the pump light source and the nonlinear optical
medium are provided the front mirror and the rear mirror of the
beam reduction system, and a color filter is arranged behind the
second nonlinear optical medium.
Description
CROSS REFERENCES
[0001] This application claims priority to Chinese Patent
Application Ser. No. CN202010964346.9 filed on 15 Sep. 2020.
TECHNICAL FIELD
[0002] The invention is related to a parametric light generation
method and its application and belongs to the technical field of
laser and nonlinear optics.
BACKGROUND ART
[0003] For now, the laser has been applied to various fields of
human society. To meet the application requirements, people usually
use nonlinear optical frequency conversion technologies to obtain
various laser wavelengths. The phase-matching technology was
developed soon after the frequency doubling phenomenon was
discovered in the 1960s, and it now has developed into the most
effective and important nonlinear optical frequency conversion
method. The phase-matching technology overall consists of two major
categories--sum frequency and difference frequency. Two
representative examples of the sum frequency are frequency doubling
and cascaded frequency tripling. Previously, all the optical
parametric frequency conversion processes with phase matching, such
as optical parametric generation, optical parametric oscillation,
and optical parametric amplification, were considered as difference
frequencies.
[0004] For the birefringent phase matching of bulk crystals and the
quasi-phase matching of periodic crystals, the following energy
conversion relationship applies:
.omega..sub.p=.omega..sub.s+.omega..sub.i (namely
.omega..sub.s=.omega..sub.p-.omega..sub.i), where: .omega..sub.s
denotes signal light, .omega..sub.p denotes pump light, and
.omega..sub.i denotes idle frequency light. It is a second-order
nonlinear optical effect and related to the second-order electric
polarizability .chi..sup.(2). For the degenerate four-wave mixing
of optical fibers, the following energy conversion relationship
applies: 2.omega..sub.p=+(D.sub.i (namely
.omega..sub.s=2.omega..sub.p-.omega..sub.i). It is a third-order
nonlinear optical effect and related to the third-order electric
polarizability .chi..sup.(3). Looking from the perspective of
signal light .omega..sub.s, all the above optical parametric
processes are generated by the difference frequencies between the
pump light .omega..sub.p and the idle frequency light
.omega..sub.i. Therefore, they share the same basic principle of
optical difference frequency.
[0005] Based on the optical difference-frequency principle,
numerous patent documents have covered the technologies on
parametric light by now. For example, the patent document
EP3273550A1 has disclosed an optical parametric waveform
synthesizer and an optical waveform synthesis method; the patent
document RU2688860C1 has disclosed a parametric light generator;
the patent document US20120134377A1 has disclosed a
polarization-entangled photon pair generator and its generation
method; the patent document U.S. Pat. No. 6,940,639B1 has disclosed
a phase-matched parametric light generation method in monolithic
integrated intersubband optical devices; the patent document
DE60000851T2 has disclosed a diode laser and the generation of
parametric light; and the patent document RU2099839C1 has disclosed
a parametric radiation generating device.
[0006] The patent document CN109739061A has disclosed a waveguide
chip that realizes nonlinear frequency conversion based on the
coupled waveguide. The kernel theory of the device is the
three-wave and four-wave nonlinear difference frequency processes.
It is to produce multiple waveguide regions and utilize the applied
electric field to adjust the phase to realize the tuning of the
output light by varying the waveguide spacing. When the pump light
wavelength is 1550 nm, and the waveguide spacing varies from 400 nm
to 900 nm, the wavelength of the entangled photons can be tuned
from 1200 nm to 2300 nm. The patent document CN101895053A has
disclosed a cascaded optical parametric conversion system and an
optical parametric conversion method. The system consists of
cascaded KTP crystals and KTA crystals, with the former used for
the type-II phase-matched optical parametric conversion process of
the pump light generated by the pumping sources and the latter used
for the noncritical phase-matched and the 90.degree. critical
phase-matched parametric conversion process of the KTP crystal
outputs. This method utilizes the KTP crystals to perform the
type-II phase-matched optical parametric conversion process for the
pump light generated by the pumping sources and the KTA crystals to
perform the noncritical phase-matched or the 90.degree. critical
phase-matched parametric conversion process for the outputs of the
KTP crystals.
[0007] All the existing technologies as mentioned above are based
on difference frequencies: when the nonlinear optical medium is a
crystal, the frequency of the signal light equals the difference in
frequency between the pump light and the idle frequency light; when
the nonlinear optical medium is a waveguide or an optical fiber,
the frequency of the signal light equals the frequency of the pump
light multiply two and minus the frequency of the idle frequency
light; the frequency conversion range is subject to the restriction
.omega..sub.s<2.omega..sub.p. For now, there is still no report
on the generation of parametric light through the sum frequency
process, especially the three-wave or above nonlinear sum
frequency. Therefore, the invention is presented.
DESCRIPTION OF THE INVENTION
[0008] As their phase-matched optical parametric frequency
conversion is all based on difference frequencies, the existing
technologies have disadvantages as follows: tunable optical
parametric frequency conversion is available in the long-wave
direction but not in the short-wave direction for the crystals
(.omega..sub.s<.omega..sub.p); the frequency conversion of the
waveguide and optical fiber can only be carried out in a limited
frequency range near the pump light
(.omega..sub.s<2.omega..sub.p), and the tuning of the signal
light depends on the tuning of the pump light. In view of such
shortcomings, the invention has presented a parametric light
generation method and its application in generating parametric
light through the sum frequency process. This method can realize
frequency up-conversion laser output easily following the basic
physical mechanism .omega..sub.s=.omega..sub.p+.omega..sub.i. Its
advantages include short-wave frequency conversion
(.omega..sub.s>.omega..sub.p), large frequency shift (w can be
larger than 2.omega..sub.p and even 3.omega..sub.p), and no tuning
of the pump light.
[0009] Term interpretation: [0010] 1. GdCOB: Abbreviation of the
gadolinium calcium oxoborate crystal; molecular formula:
GdCa.sub.4O(BO.sub.3).sub.3. [0011] 2. YCOB: Abbreviation of the
yttrium calcium oxy borate crystal; molecular formula:
YCa.sub.4O(BO.sub.3).sub.3. [0012] 3. KDP: Abbreviation of the
potassium dihydrogen phosphate; molecular formula:
KH.sub.2PO.sub.4. [0013] 4. BBO: Abbreviation of the beta barium
borate crystal; molecular formula: (3-BaB.sub.2O.sub.4. [0014] 5.
(.theta., .PHI.): The space direction denoted by the polar
coordinates, where .theta. is the angle between the direction and
the optical principal axis Z of the crystal, .PHI. is the azimuth
angle, namely the angle between the X-axis and the projection of
the direction into the XY principal plane of the crystal.
[0015] The generating mechanism of the parametric light in the
invention is as follows:
[0016] The optical parametric generation process described in the
invention follows an energy transfer mechanism as shown in FIG. 1.
FIG. 1 (A) shows the cascade transition process of the one-photon
absorption, relaxation, and sum-frequency, which is a
.chi..sup.(1)+.chi..sup.(2) effect, emits signal light with a
frequency in the range of
.omega..sub.p<.omega..sub.s.ltoreq.2.omega..sub.p, and is
referred to as the type-A sum-frequency optical parametric process
in the invention. FIG. 1 (B) shows the cascade transition process
of the two-photon absorption, relaxation, and sum-frequency, which
is a .chi..sup.(3)+.chi..sup.(2) effect, emits signal light with a
frequency in the range of
2.omega..sub.p<.omega..sub.s3.omega..sub.p, and is referred to
as the type-B sum-frequency optical parametric process in the
invention. FIG. 1 (C) shows the cascade transition process of the
three-photon absorption, relaxation, and sum-frequency, which is a
.chi..sup.(5)+.chi..sup.(2) effect, emits signal light with a
frequency in the range of
3.omega..sub.p<.omega..sub.s.ltoreq.4.omega..sub.p, and is
referred to as the type-C sum-frequency optical parametric process
in the invention. FIG. 1 (D) shows another cascade transition
process of the three-photon absorption, relaxation, and
sum-frequency. Distinguished from the first three effects, the
photons of the pump light in this effect do not participate in the
final sum frequency process directly. Instead, they will first be
relaxed into the two photons of the idle frequency
light--.omega..sub.i1 and .omega..sub.i2 and generate the photon
.omega..sub.s (2.omega..sub.p<.omega..sub.s<3.omega.) of the
signal light through sum-frequency mixing. The effect in FIG. 1 (D)
is a .chi..sup.(3)+.chi..sup.(1)+.chi..sup.(2) effect and is
referred to as the type-D sum-frequency optical parametric process
in the invention. From the perspective of signal light generation,
the above optical parametric generation processes are all
sum-frequency processes (.omega..sub.s=.omega..sub.p+.omega..sub.i
or .omega..sub.s .omega..sub.i1+.omega..sub.i2), which is
essentially distinguished from the previous difference-frequency
optical parametric generation effects. In short, the combination of
the second-order nonlinear optical effect and the photon absorption
and relaxation effect can generate effective and wide-range tunable
sum-frequency parametric light. All methods of generating
parametric light through sum frequency based on the above mechanism
or similar mechanisms and their related applications are within the
protection scope of the invention, no matter how many pump light
photons are involved and they are involved directly or
indirectly.
[0017] The technical solution of the invention is as follows:
[0018] A parametric light generation method, which comprises steps
as follows:
[0019] A nonlinear optical material that meets the sum-frequency
phase-matched conditions is provided. It shall satisfy the energy
conservation condition .omega..sub.p+.omega..sub.i=.omega..sub.s
(namely 1/.lamda..sub.p+1/.lamda..sub.i=1/.lamda..sub.s) and the
momentum conservation condition
n.sub.p.omega..sub.p+n.sub.i.omega..sub.i=n.sub.s.omega..sub.s
simultaneously, where s denotes signal light, p denotes pump light,
and i denotes idle frequency light;
[0020] Laser with a wavelength of .lamda..sub.p is injected into
the said nonlinear optical material as pump light. Then, the
material will output signal light with a wavelength of
.lamda..sub.s, namely the tunable sum-frequency parametric
light.
[0021] According to a preferred embodiment of the invention, the
sum-frequency phase-matching conditions can be changed continuously
by adjusting the space direction, temperature, voltage, or
microstructure parameters of the nonlinear optical material to
realize the continuous change of .lamda..sub.s and output the
tunable sum-frequency parametric light.
[0022] According to a preferred embodiment of the invention, light
waves with wavelengths of .lamda..sub.i and .lamda..sub.s are
generated and amplified spontaneously by the nonlinear optical
material through parametric scattering or parametric fluorescence,
instead of being input from outside. The invention refers to the
solution as "sum-frequency optical parametric generation".
[0023] According to a preferred embodiment of the invention, light
waves with wavelengths of .lamda..sub.i and .lamda..sub.s are
generated and amplified spontaneously by the nonlinear optical
material through parametric scattering or parametric fluorescence,
instead of being input from outside; in the resonant cavity formed
by adding cavity mirrors at both ends of the nonlinear optical
material, the signal light will make multiple round trips to gain
significantly enhanced output. The invention refers to the solution
as "sum-frequency optical parametric oscillation".
[0024] According to a preferred embodiment of the invention, low
energy signal light .lamda..sub.s and high energy pump light
.lamda..sub.p are provided at the input end, and they will interact
with each other on the premises of satisfying the sum-frequency
phase-matching conditions to amplify the signal light significantly
at the output end at the cost of consuming the pump light. The
invention refers to the solution as "sum-frequency optical
parametric amplification".
[0025] According to a preferred embodiment of the invention, the
said nonlinear optical material is a bulk crystal with a single
structure, a crystal with a periodic structure that can realize
quasi-phase matching, an ordinary optical fiber, or a photonic
crystal fiber.
[0026] According to a further preferred embodiment of the
invention, the said bulk crystal is GdCOB, YCOB, KDP, or BBO. By
adding rare-earth ions to these materials, the fluorescence
emissions of their characteristic wavebands can be enhanced. Then,
by designing the signal light .lamda..sub.s or the idle frequency
light .lamda..sub.i into the wavebands in combination with the
phase-matching theory, the pump threshold of the sum-frequency
optical parametric effect can be reduced to boost the output power
and output energy of the signal light and improve the conversion
efficiency.
[0027] According to a preferred embodiment of the invention, the
pulse laser (for example, the femtosecond-level ultrafast laser) is
to be used as the pump light. According to a further preferred
embodiment of the invention, the pump light is to be focalized or
reduced in beams for space shaping to boost its power density and
improve the output energy and conversion efficiency of the signal
light.
[0028] According to the invention, for the two
solutions--"sum-frequency optical parametric generation" and
"sum-frequency optical parametric amplification", the pulse laser
(such as the ultra-fast laser with pulse width less than 1 ps) is
preferred as the pumping source, and the pump light needs to be
focalized or reduced in beams for space shaping to boost its power
density and improve the output energy and conversion efficiency of
the signal light. For the solution "sum-frequency optical
parametric oscillation", the existence of the resonant cavity
greatly reduces the system's requirement for the power density of
the incident pump light, so the pumping source can be in either
pulsed operation or continuous operation. Like the two
solutions--"sum-frequency optical parametric generation" and
"sum-frequency optical parametric amplification", the solution
"sum-frequency optical parametric oscillation" can also improve the
power density of its pump light through focusing or reduction in
beams.
[0029] According to a preferred embodiment of the invention, the
1540 nm femtosecond laser is to be used as the pump light: when the
nonlinear optical material is a GdCOB crystal processed along
(.theta.=146.degree., .PHI.=0.degree.), the tunable laser output at
the visible waveband of 485-770 nm can be obtained by rotating the
crystal to adjust the sum-frequency phase-matching conditions; when
the nonlinear optical material is a YCOB crystal processed along
(.theta.=140.degree., .PHI.=0.degree.), the tunable laser output at
the visible waveband of 450-770 nm can be obtained by rotating the
crystal to adjust the sum-frequency phase-matching conditions.
[0030] According to a preferred embodiment of the invention, the
1056 nm femtosecond laser is used as the pump light, and when the
nonlinear optical material is a YCOB crystal processed along
(.theta.=149.degree., .PHI.=0.degree.), the tunable laser output at
the visible waveband of 425-528 nm can be obtained by rotating the
crystal to adjust the sum-frequency phase-matching conditions.
[0031] According to a preferred embodiment of the invention, the
1056 nm femtosecond laser is used as the pump light, and when the
nonlinear optical material is a KDP crystal processed along
(.theta.=41.degree., .PHI.=45.degree.), the tunable laser output at
the visible waveband of 390-670 nm can be obtained by rotating the
crystal to adjust the sum-frequency phase-matching conditions.
[0032] According to a preferred embodiment of the invention, the
1053 nm femtosecond laser is used as the pump light, and when the
nonlinear optical material is a .beta.-BBO crystal processed along
(.theta.=23.degree., .PHI.=30.degree.), the tunable laser output at
the visible waveband of 185-526.5 nm can be obtained by rotating
the crystal to adjust the sum-frequency phase-matching
conditions.
[0033] According to the invention, the following applications of
the parametric light generation method are also available:
[0034] The sum-frequency parametric light generation of the
lithography machine (193 nm) and the medical diagnosis and
radiation treatment (325 nm);
[0035] The dual-wavelength sum-frequency parametric light
generation of the ultraviolet differential absorption laser
radar;
[0036] The dual-wavelength sum-frequency parametric light
generation of the hemoglobin detection in carbon monoxide
poisoning;
[0037] The dual-wavelength sum-frequency parametric light
generation for the treatment of intractable port-wine stains;
[0038] The sum-frequency parametric light generation of the white
light laser.
[0039] According to the invention, a parametric light generator
which comprises a pump light source and a nonlinear optical medium
sequentially arranged along the optical path is also made
available. The said nonlinear optical material meets the
sum-frequency phase-matched conditions. That is it satisfies the
energy conservation condition
.omega..sub.p+.omega..sub.i=.omega..sub.s (namely
1/.lamda..sub.p+1/.lamda..sub.1=1/.lamda..sub.s) and the momentum
conservation condition
n.sub.p.omega..sub.p+n.sub.i.omega..sub.i=n.sub.s.omega..sub.s
simultaneously, where s denotes signal light, p denotes pump light,
and i denotes idle frequency light.
[0040] According to a preferred embodiment of the invention, a
focusing lens is also provided between the pump light source and
the nonlinear optical medium.
[0041] According to a preferred embodiment of the invention, a
color filter is also arranged behind the nonlinear optical medium
along the light path.
[0042] According to a preferred embodiment of the invention, an
input mirror of optical parametric oscillation is provided between
the focusing lens and the nonlinear optical medium along the light
path, and an output mirror of optical parametric oscillation is
provided behind the nonlinear optical medium.
[0043] According to a preferred embodiment of the invention, a
signal light source, a signal light reflecting mirror, and a beam
combiner for the pump light and the signal light are also provided
to enable the signal light generated by the signal light source to
enter the focusing lens together with the pump light generated by
the pump light source upon the reflecting of the signal light
reflecting mirror and the combining of the beam combiner for the
pump light and the signal light.
[0044] According to a preferred embodiment of the invention, behind
the nonlinear optical medium is provided the second nonlinear
optical medium along the optical path, between the pump light
source and the nonlinear optical medium are provided the front
mirror and the rear mirror of the beam reduction system, and a
color filter is arranged behind the second nonlinear optical
medium.
[0045] The theoretical core of the invention is the sum-frequency,
namely the frequency of the signal light equals the sum of the
frequency of the pump light and that of the idle frequency light.
Therefore, it can achieve frequency up-conversion, and its final
output signal light has a higher frequency and a shorter wavelength
than the pump light. The sum-frequency generator is simple in
construction, easy to operate, flexible to control, and can be
tuned to a waveband farther away from the pump light. For example,
it can realize a tunable output at the visible waveband of 400 nm
to 700 nm when the pump light wavelength is 1550 nm.
[0046] The beneficial effects of the invention are as follows:
[0047] 1. The invention presents an optical sum-frequency-based
parametric light generation method and its application to make up
for the deficiency of the past parametric light technology that can
realize difference-frequency only. With this method, people can
also realize tunable optical parametric frequency conversion toward
the short wave direction with single-wavelength pump light,
presenting a convenient, flexible, and near-perfect frequency
up-conversion way free of spectrum limits. [0048] 2. The invention
has particularly significant advantages in producing tunable
deep-ultraviolet laser light. The past technologies usually connect
in series multiple second-order nonlinear optical processes,
including the frequency doubling and frequency tripling processes
at the front end, the difference-frequency optical parametric
process at the middle-end, and the frequency doubling and
sum-frequency processes at the back end, and they need four to five
nonlinear optical media. By contrast, the installation shown in
FIG. 2 of the invention requires only one nonlinear optical medium,
so it has an obvious price advantage. Also, as it is simple in
construction, convenient to adjust, small in size, and with high
reliability, it has high commercial value. [0049] 3. The invention
opens up a new field of phase-matched optical parametric frequency
conversion technologies and has important application prospects in
industrial production, communication information, bio-medicine,
environmental testing, national defense and military, scientific
research, etc.
BRIEF DESCRIPTION OF THE FIGURES
[0050] FIG. 1 is the mechanism diagram of the sum-frequency
parametric light generation in the invention: the cascade
transition process of the one-photon absorption, relaxation, and
sum-frequency; the cascade transition process of the two-photon
absorption, relaxation, and sum-frequency; the cascade transition
process of the three-photon absorption, relaxation, and
sum-frequency; and another cascade transition process of the
three-photon absorption, relaxation, and sum-frequency.
[0051] FIG. 2 shows the diagram of the installation for the
"sum-frequency optical parametric generation" solution as described
in Embodiments 1, 3, 4, 5, 6, and 7 of the invention.
[0052] FIG. 3 shows the diagram of the installation for the
"sum-frequency optical parametric oscillation" solution described
in the invention.
[0053] FIG. 4 shows the diagram of the installation for the
"sum-frequency optical parametric amplification" solution described
in the invention.
[0054] FIG. 5 shows the spectrogram obtained via the "sum-frequency
optical parametric generation" solution based on 1540 nm pump light
and a GdCOB crystal as described in Embodiment 1 of the
invention.
[0055] FIG. 6 shows the theoretical and experimental data obtained
via the "sum-frequency optical parametric generation" solution
based on 1540 nm pump light and a GdCOB crystal as described in
Embodiment 1 of the invention.
[0056] FIG. 7 shows the diagram of the installation for the
"sum-frequency optical parametric generation" solution based on
1540 nm pump light and a GdCOB crystal as described in Embodiment 2
of the invention.
[0057] FIG. 8 shows the spectrogram obtained via the "sum-frequency
optical parametric generation" solution based on 1540 nm pump light
and a GdCOB crystal as described in Embodiment 2 of the
invention.
[0058] FIG. 9 shows the spot contrast diagram obtained via the
"sum-frequency optical parametric generation" solution based on
1540 nm pump light and a GdCOB crystal as described in Embodiment 1
and Embodiment 2 of the invention.
[0059] FIG. 10 shows the spectrogram obtained via the
"sum-frequency optical parametric generation" solution based on
1540 nm pump light and a YCOB crystal as described in Embodiment 3
of the invention.
[0060] FIG. 11 shows the theoretical and experimental data obtained
via the "sum-frequency optical parametric generation" solution
based on 1540 nm pump light and a YCOB crystal as described in
Embodiment 3 of the invention.
[0061] FIG. 12 shows the spectrogram obtained via the
"sum-frequency optical parametric generation" solution based on
1056 nm pump light and a YCOB crystal as described in Embodiment 4
of the invention.
[0062] FIG. 13 shows the theoretical and experimental data obtained
via the "sum-frequency optical parametric generation" solution
based on 1056 nm pump light and a YCOB crystal as described in
Embodiment 4 of the invention.
[0063] FIG. 14 shows the spectrogram obtained via the
"sum-frequency optical parametric generation" solution based on
1056 nm pump light and a KDP crystal as described in Embodiment 5
of the invention.
[0064] FIG. 15 shows the theoretical and experimental data obtained
via the "sum-frequency optical parametric generation" solution
based on 1056 nm pump light and a KDP crystal as described in
Embodiment 5 of the invention.
[0065] FIG. 16 shows the diagram of the installation for the
"sum-frequency optical parametric generation" solution capable of
outputting dual-wavelength signal light as described in Embodiments
8, 9, and 10 of the invention.
[0066] Where 1. Pump light source, 2. Pump light with a wavelength
of .lamda..sub.p, 3. Focusing lens, 4. Non-linear optical medium,
5. Color filter, 6. Signal light with a wavelength of
.lamda..sub.s, 7. Input mirror of optical parametric oscillation,
8. Output mirror of optical parametric oscillation, 9. Signal light
source, 10. Signal light reflecting mirror, 11. Beam combiner of
the pump light and the signal light, 12. Front mirror of the beam
reduction system, 13. Rear mirror of the beam reduction system, 14.
The first non-linear optical medium, 15. The second non-linear
optical medium.
Detailed Embodiments
[0067] The invention is further described in combination with the
attached figures and embodiments as follows, but the protection
scope of the present invention is not limited to this.
[0068] The invention presents a parametric light generation method,
which comprises steps as follows: A nonlinear optical material that
meets the sum-frequency phase-matched conditions is provided. That
is it shall satisfy the energy conservation condition
.omega..sub.p+.omega..sub.i=.omega..sub.s (namely
1/.lamda..sub.p+1/.lamda..sub.i=1/.lamda..sub.s) and the momentum
conservation condition
n.sub.p.omega..sub.p+n.sub.i.omega..sub.i=n.sub.s.omega..sub.s
simultaneously. Laser light with a wavelength of .lamda..sub.p is
injected into the said nonlinear optical material as pump light.
Then, the material will output signal light with a wavelength of
.lamda..sub.s. The sum-frequency phase-matching conditions can be
changed continuously by adjusting the space direction, temperature,
voltage, or microstructure parameters of the nonlinear optical
material to realize the continuous change of .lamda..sub.s and
output the tunable sum-frequency parametric light. On this basis,
different technical routes can be selected depending on the needs,
and the corresponding installations also vary. [0069] (1) As shown
in FIG. 2, the pump light source 1 and the focusing lens 3 are both
arranged along the optical path. Among them, the pump light source
1 is used to generate the pump light with a wavelength of
.lamda..sub.p, and the focusing lens 3 plays a focusing role to
improve the power density of the pump light 2. For the non-linear
optical medium 4, only the pump light is input from outside, and
the light waves with wavelengths of .lamda..sub.i and .lamda..sub.s
are generated and amplified spontaneously by the nonlinear optical
material through parametric scattering or parametric fluorescence.
At the end of the non-linear optical medium 4, the color filter 5
will filter out the residual pump light .lamda..sub.p and the idle
frequency light .lamda..sub.i to obtain the pure signal light 6
with a wavelength of .lamda..sub.s. The invention refers to this
solution as "sum-frequency optical parametric generation". [0070]
(2) As shown in FIG. 3, the pump light source 1 and the focusing
lens 3 are both arranged along the optical path. Among them, the
pump light source 1 is used to generate the pump light with a
wavelength of .lamda..sub.p, and the focusing lens 3 plays a
focusing role to improve the power density of the pump light 2. For
the non-linear optical medium 4, only the pump light is input from
outside, and the light waves with wavelengths of .lamda..sub.i and
.lamda..sub.s are generated and amplified spontaneously by the
nonlinear optical material through parametric scattering or
parametric fluorescence. In the resonant cavity formed by adding
cavity mirrors at both ends of the nonlinear optical material, the
signal light will make multiple round trips to gain significantly
enhanced output. The input mirror of the optical parametric
oscillation 7 presents a high transmittance for the pump light and
high reflectivity in the waveband of the signal light, and the
output mirror of the optical parametric oscillation 8 presents a
high reflectivity for the pump light and allows only part of the
signal light to pass through, so the signal light 6 with a
wavelength of .lamda..sub.s can be output. The invention refers to
this solution as "sum-frequency optical parametric oscillation".
[0071] (3) As shown in FIG. 4, arranged along the optical path, the
pump light source 1 generates the high-intensity pump light 2 with
a wavelength of .lamda..sub.p, and the signal light source 9
generates the low-intensity signal light 6 with a wavelength of
.lamda..sub.s. Upon going through the signal light reflecting
mirror 10 and the beam combiner of the pump light and the signal
light 11, the signal light will be combined with the pump light 2
with a wavelength of .lamda..sub.p (the signal light reflecting
mirror 10 presents a high reflectivity for the signal light, and
the beam combiner for the pump light and the signal light 11
presents a high reflectivity for the signal light and high
transmittance for the pump light). The combined light then is
focalized into the non-linear optical medium 4 by the focusing lens
3. .lamda..sub.p and .lamda. will interact with each other on the
premises of satisfying the sum-frequency phase-matching conditions
to amplify the signal light significantly at the output end at the
cost of consuming the pump light. The color filter 5 will filter
out the residual pump light .lamda..sub.p and the newly generated
idle frequency light .lamda. to obtain the pure and high-energy
signal light 6 with a wavelength of .lamda..sub.s. If the signal
light source 9 is tunable in wavelengths, the signal light with
high energy and tunable wavelengths can be obtained at the output
end, by adjusting the sum-frequency phase-matching conditions of
the non-linear optical medium 4 according to the wavelengths of the
signal light source 9. The invention refers to the solution as
"sum-frequency optical parametric amplification".
[0072] The focusing lens 3 in the above three solutions can be
replaced by an optical beam reduction system formed by two convex
lenses with different focal lengths to improve the beam quality of
the output light and reduce divergence.
[0073] Based on the three representative technical solutions above,
a low-cost, miniaturized, wide-band tunable, precise, reliable,
simple and effective frequency up-conversion laser device can be
produced. Its signal light can meet the needs for tunable laser
light in many fields. All sum-frequency parametric light generation
methods based on the sum-frequency optical parametric generation
mechanism as described in the invention and derived from the above
solutions, as well as the related applications thereof, are within
the scope of protection of the invention.
Embodiment 1
[0074] A "sum-frequency optical parametric generation" solution
with a GdCOB crystal pumped by a 1540 nm laser as the non-linear
optical medium, which follows the mechanism as shown in B and C of
FIG. 1. The installation is as shown in FIG. 2, with all parts
arranged along the optical path. Among them, the pump light source
1 is an ultrafast laser with a wavelength of 1540 nm, a pulse width
of 160 fs, and a repeated frequency of 100 kHz, the focusing lens 3
is with a 200 mm focal length, the non-linear optical medium 4 is a
GdCOB crystal with the size of 6.times.6.times.10 mm.sup.3 and
processed along (.theta.=146.degree., .PHI.=0.degree.), and the
color filter 5 presents a high reflectivity for the wavelength 1540
nm and high transmittance for the waveband 300-800 nm. The test
result of the solution is shown in FIG. 5 and FIG. 6.
[0075] FIG. 5 shows the signal light spectra obtained in different
positions when the GdCOB crystal is rotated, where Figure A is the
spectrum of the pump light (.lamda..sub.p=1540 nm), and Figure B is
the spectrum of the frequency doubling output (.lamda..sub.p=770
nm) realized during the normal incidence of the crystal. The light
path of the pump light in the crystal can be continuously changed
by rotating the GdCOB crystal to satisfy the different
sum-frequency phase-matching conditions, thereby realizing the
continuous change of the wavelength .lamda..sub.s of the signal
light and the output of the tunable sum-frequency parametric light.
Based on the refraction law, the direction of light propagation
within the crystal can be calculated from the external rotation
angle of the crystal. Figures C through to H show the spectra of
the signal light obtained in several representative directions,
namely .theta.=149.4.degree., 151.1.degree., 153.3.degree.,
156.0.degree., 157.8.degree., and 161.5.degree.. The .PHI. is fixed
as 0.degree., namely the crystal is rotated in its XZ principal
plane only. The test results show that the installation can
generate sum-frequency parametric light of 485-770 nm.
[0076] FIG. 6 (A) shows the sum-frequency phase-matching curve
(1/.lamda..sub.p+1/.lamda..sub.i=1/.lamda..sub.s, where:
.lamda..sub.v=1540 nm, .lamda..sub.s denotes the bottom
X-coordinate, the corresponding .lamda..sub.i denotes the top
X-coordinate, and the Y-coordinate is the phase-matching angle
.theta.) calculated for Embodiment 1, as well as the corresponding
experimental points. As can be seen from Figure A, the theoretical
results agree well with the measured values, thus confirming that
this effect is a sum-frequency process. In addition, as the pump
light polarizations are observed to be mutually perpendicular to
the signal light polarizations, this phase matching turns out to be
type-I. Figure B shows the relationship between the effective
nonlinear optical coefficient d.sub.eff and the wavelength
.lamda..sub.s of the signal light. As can be seen from Figure B,
the d.sub.eff increases along with the .lamda..sub.s. Such a
calculated law agrees with the experimental law obtained in Figure
C, namely the output power and conversion efficiency of the signal
light increases with the increase of the .lamda..sub.s and, at the
same time, the pump threshold reduces. Figure D shows the change
relationship between the output power of the signal light and that
of the pump light when .lamda..sub.s=622 nm: the pump threshold is
86 mW, and the corresponding pump power density is 826 MW/cm.sup.2;
under the 124 mW pump power, the signal light output is 3.7 mW, and
the optical conversion efficiency is 3.0%. If the pump light source
and the non-linear optical medium are kept unchanged, the
"sum-frequency optical parametric oscillation" solution in FIG. 3
can reduce the pump threshold and further improve the output power
and conversion efficiency.
Embodiment 2
[0077] A "sum-frequency optical parametric generation" solution
with a GdCOB crystal pumped by a 1540 nm laser as the non-linear
optical medium, which follows the mechanism as shown in B and C of
FIG. 1. The installation is as shown in FIG. 7, with all parts
arranged along the optical path. Distinguished from that in FIG. 2,
this installation uses an optical beam reduction system formed by
two convex lenses with different focal lengths to replace the
focusing lens 3. The pump light beam reduction system comprises the
front mirror 12 and the rear mirror 13 in replacement of the
focusing lens 3 as shown in FIG. 2. Therefore, the incident pump
light beam of the crystal has better parallelism.
[0078] Among them, the pump light source 1 is an ultrafast laser
with a wavelength of 1540 nm, a pulse width of 160 fs, and a
repeated frequency of 100 kHz; the focal lengths of the front
mirror 12 and the rear mirror 13 of the beam reduction system are
300 mm and 100 mm respectively, so the beam reduction ratio is 3:1;
the non-linear optical medium 4 is a GdCOB crystal with the size of
6.times.6.times.10 mm.sup.3 processed along (.theta.=146.degree.,
.PHI.=0.degree.); and, the color filter 5 presents a high
reflectivity for the wavelength 1540 nm and high transmittance for
the waveband 300-800 nm.
[0079] The test result of the solution is shown in FIG. 8. It shows
the signal light spectra obtained in different positions when the
GdCOB crystal is rotated. The light path of the pump light in the
crystal can be continuously changed by rotating the GdCOB crystal
to satisfy the different sum-frequency phase-matching conditions,
thereby realizing the continuous change of the wavelength .lamda.
of the signal light and the output of the tunable sum-frequency
parametric light. The test results show that the installation can
be used to generate sum-frequency parametric light of 490-770 nm.
As the crystal sample used in the test has good parallelism at the
two end faces and can form partial resonant cavity under uncoated
conditions, which is conducive to the output of frequency-doubled
light in the tangential direction (namely in the frequency doubling
direction of 1540 nm), frequency doubling signals with a wavelength
of 770 nm are detected, more or less, in each spectrum. If
frequency-doubled light is undesirable, the frequency-doubled
signals in the tunable output may be eliminated through such
technological means as reducing the parallelism of the end faces of
the crystal, coating the two end faces with fundamental-frequency
antireflective (AR) film, and coating the output end with the
frequency-doubled high-reflective (HR) film.
[0080] FIG. 9 shows the light spot images of the installation in
FIG. 2 and that in FIG. 7, among which Figure A shows the light
spot of the signal light (.lamda..sub.s=497 nm) obtained by the
installation in FIG. 2, and Figure B shows the light spot of the
signal light (.lamda..sub.s=490 nm) obtained by the installation in
FIG. 7. The comparison shows that the pump light beam reduction
solution is more beneficial to obtaining light spots with higher
beam quality.
Embodiment 3
[0081] A "sum-frequency optical parametric generation" solution
with a YCOB crystal pumped by a 1540 nm laser as the non-linear
optical medium, which follows the mechanism as shown in B of FIG.
1. The installation is as shown in FIG. 2, with all parts arranged
along the optical path. Among them, the pump light source 1 is an
ultrafast laser with a wavelength of 1056 nm, a pulse width of 160
fs, and a repeated frequency of 100 kHz, the focusing lens 3 is
with a 200 mm focal length, the non-linear optical medium 4 is a
YCOB crystal with the size of 4.times.4.times.10 mm.sup.3 and
processed along (.theta.=149.degree., .PHI.=0.degree.), and the
color filter 5 presents a high reflectivity for the wavelength 1064
nm and high transmittance for the waveband 300-800 nm. The test
results of the solution are shown in FIG. 10 and FIG. 11.
[0082] FIG. 10 shows the signal light spectra obtained in different
positions when the YCOB crystal is rotated, where Figure A is the
spectrum of the pump light (.lamda..sub.p=1540 nm), and Figure B is
the spectrum of the frequency doubling output (.lamda..sub.s=770
nm) realized during the normal incidence of the crystal. The light
path of the pump light in the crystal can be continuously changed
by rotating the YCOB crystal to satisfy the different sum-frequency
phase-matching conditions, thereby realizing the continuous change
of the wavelength .lamda..sub.s of the signal light and the output
of the tunable sum-frequency parametric light. Based on the
refraction law, the direction of light propagation within the
crystal can be calculated from the external rotation angle of the
crystal. Figures C through to H show the spectrums of the signal
light obtained in several representative directions, namely
.theta.=142.8.degree., 144.6.degree., 147.0.degree., and
149.8.degree.. The .PHI. is fixed as 0.degree., namely the crystal
is rotated in its XZ principal plane only. The test results show
that the installation can generate sum-frequency parametric light
of 450-770 nm.
[0083] FIG. 11 shows the sum-frequency phase-matching curve
(1/.lamda..sub.p+1/.lamda..sub.i=1/.lamda..sub.s, where:
.lamda..sub.p=1540 nm, .lamda..sub.s denotes the bottom
X-coordinate, the corresponding .lamda..sub.i denotes the top
X-coordinate, and the Y-coordinate is the phase-matching angle
.theta.) calculated for Embodiment 3, as well as the corresponding
experimental points. As can be seen from FIG. 11, the theoretical
results agree well with the measured values, thus confirming that
this effect is a sum-frequency process. In addition, as the pump
light polarizations are observed to be mutually perpendicular to
the signal light polarizations, this phase matching turns out to be
type-I. If the pump light source and the non-linear optical medium
are kept unchanged, the "sum-frequency optical parametric
oscillation" solution in FIG. 3 can reduce the pump threshold and
further improve the output power and conversion efficiency.
Embodiment 4
[0084] A "sum-frequency optical parametric generation" solution
with a YCOB crystal pumped by a 1056 nm laser as the non-linear
optical medium, which follows the mechanism as shown in B and C of
FIG. 1. The installation used is similar to that shown in FIG. 2,
with all parts arranged along the optical path. Among them, the
pump light source 1 is an ultrafast laser with a wavelength of 1540
nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz,
the focusing lens 3 is with a 200 mm focal length, and the
non-linear optical medium 4 is a YCOB crystal with the size of
6.times.6.times.10 mm.sup.3 and processed along
(.theta.=140.degree., .PHI.=0.degree.). As there is no suitable
color filter, the solution uses no color filter 5. The test result
of the solution is shown in FIG. 12 and FIG. 13.
[0085] FIG. 12 shows the signal light spectra obtained in different
positions when the YCOB crystal is rotated, where Figure A is the
spectrum of the pump light (.lamda..sub.p=1056 nm), and Figure B is
the spectrum of the frequency doubling output (.lamda..sub.s=528
nm) realized during the normal incidence of the crystal. The light
path of the pump light in the crystal can be continuously changed
by rotating the YCOB crystal to satisfy the different sum-frequency
phase-matching conditions, thereby realizing the continuous change
of the wavelength .lamda..sub.s of the signal light and the output
of the tunable sum-frequency parametric light. Based on the
refraction law, the direction of light propagation within the
crystal can be calculated from the external rotation angle of the
crystal. Figures C through to F show the spectra of the signal
light obtained in several representative directions, namely
.theta.=150.6.degree., 152.5.degree., 154.9.degree., and
157.3.degree.. The .PHI. is fixed as 0.degree., namely the crystal
is rotated in its XZ principal plane only. The test results show
that the installation can generate sum-frequency parametric light
of 425-528 nm.
[0086] FIG. 13 shows the sum-frequency phase-matching curve
(1/.lamda..sub.p+1/.lamda..sub.i=1/.lamda..sub.s, where:
.lamda..sub.p=1056 nm, .lamda..sub.s denotes the bottom
X-coordinate, the corresponding .lamda..sub.i denotes the top
X-coordinate, and the Y-coordinate is the phase-matching angle
.theta.) calculated for Embodiment 4, as well as the corresponding
experimental points. As can be seen from FIG. 13, the theoretical
results agree well with the measured values, thus confirming that
this effect is a sum-frequency process. In addition, as the pump
light polarizations are observed to be mutually perpendicular to
the signal light polarizations, this phase matching turns out to be
type-I. If the pump light source and the non-linear optical medium
are kept unchanged, the "sum-frequency optical parametric
oscillation" solution in FIG. 3 can reduce the pump threshold and
further improve the output power and conversion efficiency.
Embodiment 5
[0087] A "sum-frequency optical parametric generation" solution
with a KDP crystal pumped by a 1056 nm laser as the non-linear
optical medium, which follows the mechanism as shown in A, B, and D
of FIG. 1. The installation used is similar to that shown in FIG.
2, with all parts arranged along the optical path. Among them, the
pump light source 1 is an ultrafast laser with a wavelength of 1056
nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz,
the focusing lens 3 is with a 200 mm focal length, and the
non-linear optical medium 4 is a KDP crystal with the size of
50.times.30.times.13 mm.sup.3 and processed along
(.theta.=41.degree., .PHI.=45.degree.). As there is no suitable
color filter, the solution uses no color filter 5. The test results
of the solution are shown in FIG. 14 and FIG. 15.
[0088] FIG. 14 shows the signal light spectra obtained in different
positions when the YCOB crystal is rotated, where Figure A is the
spectrum of the pump light (.lamda..sub.p=1056 nm), and Figure B is
the spectrum of the frequency doubling output (.lamda..sub.s=528
nm) realized during the normal incidence of the crystal. The light
path of the pump light in the crystal can be continuously changed
by rotating the KDP crystal to satisfy the different sum-frequency
phase-matching conditions, thereby realizing the continuous change
of the wavelength .lamda..sub.s of the signal light and the output
of the tunable sum-frequency parametric light. Based on the
refraction law, the direction of light propagation within the
crystal can be calculated from the external rotation angle of the
crystal. Figures C through to E show the spectra of the signal
light obtained in several representative directions, namely
.theta.=42.6.degree., 43.7.degree., and 44.4.degree.. The .PHI. is
fixed as 45.degree.. The test results show that the installation
can generate sum-frequency parametric light with .lamda..sub.s of
390-670 nm.
[0089] FIG. 15 shows the sum-frequency phase-matching curve
(1/.lamda..sub.p+1/.chi..sub.i=1/.chi..sub.s, where:
.lamda..sub.p=1056 nm, .lamda. denotes the bottom X-coordinate, the
corresponding .chi..sub.i denotes the top X-coordinate, and the
Y-coordinate is the phase-matching angle .theta.) calculated for
Embodiment 5, as well as the corresponding experimental points. The
two refractive index dispersion equations from the literature "F.
Zernike, J. Opt. Soc. Am. 54, 1215-1220, 1964" and "D. Eimerl,
Ferroelectrics. 72, 95-139, 1987" are used as the basis for
calculation, and the calculated results are presented by the solid
line and the dotted line respectively. As can be seen from the
figure, the theoretical results agree well with the measured
values, on the whole, thus confirming that this effect is a
sum-frequency process. Based on the recorded output light spectra,
more experimental points can be obtained. As shown in Figure B, the
sum-frequency theoretical calculations also agree well with the
experimental value, which further confirms that this effect is a
sum-frequency process. Additionally, another signal light
.lamda..sub.s' is also found in the experiment, and its generation
mechanism corresponds to the Figure D in FIG. 1, namely
1/.lamda..sub.i1'+1/.lamda..sub.i2'=1/.lamda..sub.s'. As shown in
Figures C and D, when .lamda..sub.s changes from 397 nm to 484 nm,
.lamda..sub.s' changes from 447 nm to 518 nm; the corresponding
.lamda..sub.i1' varies within 536-803 nm, and the .lamda..sub.i2'
within 2681-1458 nm. If the pumping source and the non-linear
optical medium are kept unchanged, the "sum-frequency optical
parametric oscillation" solution in FIG. 3 can reduce the pump
threshold and further improve the output power and conversion
efficiency.
Embodiment 6
[0090] A "sum-frequency optical parametric generation" solution
with a BBO crystal pumped by a 1053 nm laser as the non-linear
optical medium. The installation used is similar to that shown in
FIG. 2, with all parts arranged along the optical path. Among them,
the pump light source 1 is a Yb.sup.3+ ultrafast laser with a
wavelength of 1053 nm, the focusing lens 3 is with a 300 mm focal
length, and the non-linear optical medium 4 is a BBO crystal with
the size of 10.times.10.times.10 mm.sup.3 and processed along
(.theta.=45.8.degree., .PHI.=30.degree.), a direction in which the
wavelength of the sum-frequency signal light is 236 nm. When the
crystal is rotated in the plane of .PHI.=30.degree., with the
exterior angle changing from +30.degree. to -30.degree. around the
normal incidence direction, the sum-frequency phase-matching angle
in the crystal also changes from 62.9.degree. to 28.7.degree., and
the corresponding tunable range of .lamda. is 185-395 nm, covering
the entire UV band that can propagate in the air. Such a tunable
light source can meet the various demands for ultraviolet coherent
light. For example, the 193 nm light can be used as the ultraviolet
light source in the lithography, and the 325 nm light can replace
the large-volume and high-noise He--Cd ion laser for medical
diagnosis and irradiating treatment, such as checking the five
sense organs for cancer and acupoint radiation to treat
hypertension and chronic hepatitis, etc.
Embodiment 7
[0091] A "sum-frequency optical parametric generation" solution
used for the tunable frequency conversion of ultrafast and
ultra-intense lasers. The installation used is similar to that
shown in FIG. 2, with all parts arranged along the optical path.
Among them, the pump light source 1 is an ultrafast and
ultra-intense laser with a wavelength of 1053 nm and a peak power
between TW and EW. As the pumping source has a high power density
already, it needs no focusing. Therefore, the focusing lens 3 is
omitted. The non-linear optical medium 4 is a KDP crystal with a
thickness of 10 mm. Its sectional area depends on the diameter of
the installation and varies between 100.times.100 mm.sup.2 and
500.times.500 mm.sup.2. Its tangent angle is (.theta.=46.2.degree.,
.PHI.=45.degree.), a direction in which the wavelength of the
sum-frequency signal light is 660 nm and 370 nm. When the crystal
is rotated in the plane of .PHI.=45.degree., with the exterior
angle changing from +7.5.degree. to -7.5.degree. around the normal
incidence direction, the sum-frequency phase-matching angle in the
crystal also changes from 51.2.degree. to 41.2.degree., and the
corresponding tunable range of .lamda..sub.s is 318-710 nm,
covering the entire visible waveband. Such an installation can be
used for laser fusion, studies of ultrarelativistic phenomena, and
laboratory astrophysics.
Embodiment 8
[0092] A dual-wavelength sum-frequency optical parametric generator
used for ultraviolet differential absorption laser radars. Its
construction is as shown in FIG. 16, with all parts arranged along
the optical path. Among them, the pump light source 1 is a
Yb.sup.3+ ultrafast laser with a wavelength of 1053 nm, and the
focal lengths of the front mirror 12 and the rear mirror 13 of the
beam reduction system are 300 mm and 100 mm respectively. The first
non-linear optical medium 14 is a BBO crystal with a size of
10.times.10.times.10 mm.sup.3 and a tangent angle of
(.theta.=43.degree., .PHI.=30.degree.), a direction in which the
wavelength of the sum-frequency signal light is 250 nm, while the
second non-linear optical medium 15 is a BBO crystal with a size of
10.times.10.times.10 mm.sup.3 and a cutting angle of
(.theta.=30.degree., .PHI.=30.degree.), a direction in which the
wavelength of the sum-frequency signal light is 370 nm. Since the
wavelengths 250 nm and 370 nm correspond to the absorption peak and
valley of ozone respectively, this dual-wavelength light source can
be used in UV differential absorption laser radars to accurately
measure the ozone concentration in the stratosphere. In addition,
by adjusting the directions or temperatures of the two crystals,
the output wavelengths can be tuned to conduct UV differential
absorption measurement for other gases conveniently and
flexibly.
Embodiment 9
[0093] A dual-wavelength sum-frequency optical parametric generator
used for hemoglobin detection of carbon monoxide poisoning. Its
construction is as shown in FIG. 16, with all parts arranged along
the optical path. Among them, the pump light source 1 is an
ultrafast laser with a wavelength of 1550 nm, and the focal lengths
of the front mirror 12 and the rear mirror 13 of the beam reduction
system are 300 mm and 100 mm respectively. The first non-linear
optical medium 14 is a GdCOB crystal with a size of
10.times.10.times.10 mm.sup.3 and a tangent angle of
(.theta.=156.degree., .PHI.=0.degree.), a direction in which the
wavelength of the sum-frequency signal light is 555 nm, while the
second non-linear optical medium 15 is a YCOB crystal with a size
of 10.times.10.times.10 mm.sup.3 and a tangent angle of
(.theta.=147.degree., .PHI.=0.degree.), a direction in which the
wavelength of the sum-frequency signal light is 540 nm. Since the
wavelengths 555 nm and 540 nm basically correspond to the
absorption peak and valley of carbonyl hemoglobin respectively,
this dual-wavelength light source can be used to detect carbonyl
hemoglobin, thus determining the extent of carbon monoxide
poisoning. In addition, by adjusting the directions or temperatures
of the two crystals, the output wavelengths can be tuned to measure
the blood content of alcohol and other substances conveniently and
flexibly.
Embodiment 10
[0094] A dual-wavelength sum-frequency optical parametric generator
used to treat intractable port-wine stains. Its construction is
similar to that in FIG. 7, with all parts arranged along the
optical path. Among them, the pump light source 1 is a Yb.sup.3+
ultrafast laser with a wavelength of 1053 nm, and the focal lengths
of the front mirror 12 and the rear mirror 13 of the beam reduction
system are 300 mm and 100 mm respectively. The non-linear optical
medium 4 is a KDP crystal with a size of 10.times.10.times.10
mm.sup.3 and a tangent angle of (.theta.=42.5.degree.,
.PHI.=45.degree.), a direction in which the wavelength of the
sum-frequency signal light is 595 nm. The color filter 5 is omitted
here, so the remaining pump light is output together with the
signal light to form a 1053 nm and 595 nm dual-wavelength laser.
The 595 nm light can be specifically absorbed by the oxyhemoglobin
in blood vessels to form methemoglobin instantly The methemoglobin
can hardly absorb the 595 nm light, but can absorbed the 1053 nm
light. Such a synergistic thermal effect can greatly improve the
therapeutic effect of the intractable port-wine stains and reduce
adverse reactions. In addition, by adjusting the direction or
temperature of the KDP crystal, the wavelengths of the signal light
can be tuned to treat other skin complaints conveniently and
flexibly.
Embodiment 11
[0095] A sum-frequency optical parametric generator capable of
outputting white light. Its construction is as shown in FIG. 16,
with all parts arranged along the optical path. Among them, the
pump light source 1 is an ultrafast laser with a wavelength of 1550
nm, and the focal lengths of the front mirror 12 and the rear
mirror 13 of the beam reduction system are 300 mm and 100 mm
respectively. The first non-linear optical medium 14 is a BBO
crystal with a size of 10.times.10.times.10 mm.sup.3 and a tangent
angle of (.theta.=24.4.degree., .PHI.=30.degree.), a direction in
which the wavelength of the sum-frequency signal light is 445 nm,
while the second non-linear optical medium 15 is a BBO crystal with
a size of 10.times.10.times.10 mm.sup.3 and a tangent angle of
(.theta.=21.3.degree., .PHI.=30.degree.), a direction in which the
wavelength of the sum-frequency signal light is 580 nm. The
wavelengths 445 nm and 580 nm can realize white light output by
superimposing with each other. In addition, by adjusting the
directions or temperatures of the two crystals, the output
wavelengths can be tuned to adjust the color temperature of the
white light conveniently and flexibly.
* * * * *